How can I fix this Armature?
Thanks for your reply,
but it looks like the FBX exporter has exported the asset wrong.
I have an project in Unity where my fbx of original asset is broken, i was trying to export the asset object as fbx but if i import it in blender it shows like upper. BTW the Armature list shown as here, any idea how i can change this?:

Oh after fbx export i used fbx converter from autodesk to convert them to binary fbx file.